Field of the Invention
This invention relates to multi-rate processing of digital audio, and more particular to techniques for compensating amplitude and phase artifacts caused by audio processing in the lowest frequency subband.
Description of the Related Art
Audio reproduction hardware that supports high sampling rate content is currently in use. However, audio processing techniques may not be required to process the full bandwidth of such content. Because audio processing at higher sampling rates requires greater computational resources, it is undesirable to perform audio processing designed for lower sampling rates at higher sampling rates. This is especially critical for systems having limited computational resources.
Various audio processing techniques use multi-rate processing because of its computational advantages. In general, multi-rate subband processing includes subband decomposition, decimation, and expansion processes. These processes allow signals to be processed at reduced sampling rates corresponding to the bandwidth of the subbands while preserving the full bandwidth of the original content in the reconstruction phase.
Some techniques apply audio processing only to the lowest frequency subband of the subbands in order to reduce computational complexity. However, performing audio processing in the lowest frequency subband often causes amplitude and phase changes. Existing techniques attempt to correct for these changes by adding compensation filters in the higher frequency subbands that match amplitude and phase in the transition band of the subbands. Existing techniques rely on either a priori knowledge of the audio processing to calculate the compensation filters or non-real-time measurements of amplitude/phase characteristics of the processing in the transition band of the subbands.